Apparatus for maintaining balanced mud circulation to prevent blowouts



P1 H. GRIFFIN APPARATUS FOR MAINTAINING BALANCED MUD Aug. 29, 1967 l" CIRCULATION To PREVENT BLowoUTs 'Filed July 2 9, 1965 INVENTOR ATTORNEY United states Patent o s 33s 319 APPARATUS FOR MAITAINING BALANCED MUD CIRCULATION To PREVENT BLOW- This invention relates to new and useful improvements in mud circulating systems for oil wells and the principal object of the invention is to facilitate a simple and eflicient well killing procedure under conditions when the formation pressure at the bottom of the hole exceeds the hydrostatic pressure of the mud column within the hole and formation fluids flow into the well bore.

Such formation uids, which may be gas, oil, water, or combinations thereof, have low densities and the pressure difference which caused their ow becomes even greater as these extraneous fluids rise in the well bore, displacing drilling mud out the top of the well. When this occurs, a blowout is imminent unless the pressure difference which caused the formation fluid flow into the well bore is eliminated, as for example, by closing a blowout preventer such as is usually provided at the top of the well. Closing the blowout preventer traps in the well bore both the remaining mud and the foreign uids and the formation will continue to produce until the pressure in the well bore becomes equal to the formation pressure, at which time fluid ow from the formation will cease. The driller is then faced with the problem of replacing the 10W density liquid column in the well bore with a column of suflicient density to overcome the formation pressure.

In accordance with the invention the mud circulating system is adapted to pump into the well at a constant rate with a constant pressure, the theory being that in order to pump against pressure existing in the bottom of the well it is necessary that the bit below the drill stem be equal to the sum of the hydrostatic pressure of the mud column in the drill stern plus friction losses in the drill stem at the circulated rate. Thus, with a proper rate and proper pressure selected and `constantly maintained by the system of the invention, the well killing procedure becomes automatic and free of human error.

With the foregoing more important object and features in view and such other objects and features as may becorne apparent as this specification proceeds, the invention will be understood from the following description taken in conjunction with the accompanying drawing.

The drawing is a diagrammatical illustration of the mud circulating system of the invention.

Referring now to the accompanying drawing in detail, the well bore 5 having the usual casing 6 contains the drill stem 7 provided at its lower end with a bit 8, the stem 7 being turned by a rotary table 9 of the derrick 10. Drilling mud is pumped from a mud pit 11 by a positive displacement pump 12 through a mud delivery line 13 and hose 14 into the drill stem 7, being discharged out of the bit 8 into the well bore 5 and returned from the top of the casing 6 by a mud return line 15 to the mud pit 11, all in accordance with conventional practice. A manually openable and closable blowout preventer 16 of any suitable conventional type is provided at the upper end of the casing, as shown.

In accordance with the invention the positive displacement pump 12 is operated to produce a mud volume and pressure greater than is necessary to create a predetermined rate and pressure in the mud delivery line 13, such pressure being indicated by a suitable gauge 17 in the line. However, a by-pass line 18 extends from the mud delivery line 13 at a point downstream from the pump 12, the by-pass line 18 being provided with a suitable 3,338,319 Patented Aug. 29, 1967 throttling valve 19 and discharging into a iiow rate measuring device 20, hereinafter more particularly described, said iiow rate measuring device serving to measure the bypassed rate.

The throttling valve 19 is actuated by suitable pressure sensing means 21 provided in the mud delivery line 13 at a point downstream from the connection of the bypass line 18 to the line 13. The throttling valve 19 is coupled to the pressure sensing means 21 by a suitable operative connection 22, the arrangement being such that when the pressure of mud delivered by the pump 12 through the line 13 rises above a predetermined point, the sensing device 21 actuates the throttling valve 19 so as to permit more mud to be by-passed from the line 13 through the by-pas line 18 to the device 20, thus lowering the mud pressure in the delivery line 13 thereby reducing the pump rate into the drill pipe. Conversely, if the mud pressure in the line 13 falls below a predetermined point, the throttling valve restricts the mud flow throw the by-pass line 18 so that the mud pressure in the line 13 is increased and the pump rate into the drill pipe is increased. It may be noted at this time that the valve 19 is a throttling valve as such, which does not have a fully closed position but opens to a greater or lesser degree to correspondingly increase or decrease the mud ow through the by-pass line 18.

The aforementioned flow rate measuring device 20 may be of any'suitable type and for illustrative purposes it is represented by a vertical tank 23 into which the bypass line 18 discharges, the tank being provided at one side thereof with a V-shaped outlet opening 24 through which mud may run out of the tank into the mud pit 11, as indicated at 25. As long as the mud flows into the tank through the line 18 at a constant rate, a constant mud level 26 will be maintained in the tank, but if the throttling valve 19 responds to variations of mud pressure in the delivery line 13 as sensed by the means 21, so as to increase or decrease the rate of mud flow into the tank, the mud level 26 in t-he tank will adjust itself accordingly. A mud level sensing device 28 is actuated by a iioat 29 on the mud level in the tank and serves to control, as through an operative connection 30, a throttling valve 31 which is provided in the mud return line 1'5. The arrangement is such that if the mud flow through the bypass line 18 into the tank 23 should increase, the throttling valve 31 in the mud return line 15 will open to a greater extent, thus permitting more mud to iiow from the well into the pit 11. The increased ii'ow from the Well reduces the back pressure against which the drill pipe fluid is discharging permitting a drill pipe rate increase to bring the drill pipe pressure down readjustin-g throttle valve 19 to reduce the excess by-pass rate and restore the predetermined drill pipe rate. Conversely, if the flow of by-passed mud into the tank 23 should decrease, the valve 31 will restrict the return of mud through the line 15. Like the valve 19, the throttling valve 31 does not have a fully closed position but merely opens to a greater or lesser extent. A suitable pressure gauge 32 is provided in the return line 15 between the well and the valve 31.

It will be apparent from the foregoing that when the circulating system of the invention is in operation, the throttling valve 31 in the mud return line 15 may be used to maintain at 32 a pressure which, when added to the hydrostatic pressure in the well bore, is equal to or slightly greater than the pressure of extraneous iiuids in the well formation.

The driller may determine in advance the rate and pressure of the mud to be circulated through the delivery line 13 and drill stem 7, and once this predetermined rate and pressure is indexed into the system, the system will operate automatically to hold the rate and pressure at 17.

With the drill stern rate and pressure chosen and constantly held by the means 19', 20, 2.1, the rate and pressure through the mud return line will always adjust itself through the means 28, 29, 31 to what is necessary to hold the proper rate and pressure t-hrough the drill stem, thus making the well killing procedure automatic and free of human error.

While in the fore-going there has been described and shown the preferred embodiment of the invention, various modications may become apparent to those skilled in the art to which the invention relates. Accordingly, it is not desired to limit the invention to this disclosure and various modifications and equivalents may be resorted to, falling within the spirit and scope of the invention as claimed.

What is claimed as new is:

1. In a well mud circulating system includingy a drill stem discharging mud into a well bore, a mud return line extending from the well bore to a mud pit and a mud delivery line extending from the mud pit to the drill stern, apparatus for maintaining balanced mud circulation in said system to prevent blowout of the well by pressure of extraneous uids in the well bore, said apparatus comprising a positive displacement pump provided in said mud delivery line and having a capacity greater than that necessary to maintain ow of mud to said drill stem at a predetermined rate and pressure, means connected to said mud delivery line downstream from said pump and lresponsive to mud pressure in said delivery line for by-passing mud from the delivery line to the mud pit at a ow rate coordinated to maintain the rate and pressure of mud delivered to the drill stem at a predetermined constant, a mud throttling valve provided in sa-id mud return line, and means responsive to the flow rate of the by-passed mud for actuating said throttling valve whereby to proportionately increase and decrease the flow rate and pressure of mud in said return line in coordination with increase and decrease in the flow rate of the by-passed mud.

2. The system as defined in claim 1 wherein said mud by-passing means include a by-pass line connected to said mud delivery line downstream from said pump, a throttling valve provided in said by-pass line for controlling the rate of mud flow therethrough, and pressure sensing means provided in said mud delivery line downstream from said by-pass line, said pressure sensing means being operatively connected to said throttling valve in the bypass line.

3. The system as defined in claim 1 wherein said means for actuating said throttling valve in said mud return line include means for sensing the flow rate of mud through said by-passing means.

4. The system as defined in claim 1 wherein said means for actuating said throttling valve in said mud return line include a container having a by-passed mud inlet and an outlet discharging into said mud pit in coordination with said inlet whereby the mud level in said container may remain substantially constant, and means responsive to mud level variations in said container for actuating said mud return lline throttling valve.

5. The system as dened in claim 1 wherein said mud by-passing means include a by-pass line connected to said mud delivery line downstream from said pump, a throttling valve provided in said by-pass line for controlling the rate of mud flow therethrough, and pressure sensing means provided in said delivery line downstream from said by-pass line, said pressure sensing means bei-ng operatively connected to said throttling valve in the bypass line, said means for actuating said throttling valve in said mud return line including means for sensing the ow rate of mud through said by-pass line.

6. The system as defined in claim 5 wherein said flow rate sensing means include a container having a by-passed mud inlet in communication with said by-pass line and having a mud outlet discharging into said mud pit in coordination with the mud inlet whereby the mud level in said container may remain substantially constant, and means responsive to mud level variations in said container for actuating said mud return line throttling valve.

7. In a well mud circulating system including a drill stem discharging mud into a well bore, a mud return line extending from the well bore to a mud pit and a mud delivery line extending from the mud pit to the drill stem, apparatus for maintaining balanced mud circulation in said system to prevent blowout of the well by pressure of extraneous fluids in the well formation, said apparatus comprising a positive displacement pump provided in said mud delivery line and having a capacity greater than that necessary to maintain ow of mud to said drill stem at a predetermined rate and pressure, a mud by-pass line connected to said delivery line downstream from said pump, a throttling valve provided in said by-pass line for controlling the rate of mud ow therethrough, pressure sensing means provided in said delivery line `downstream from said by-pass line and operatively connected to said by-pass line throttling valve whereby to maintain substantially constant predetermined ow rate and pressure of mud delivered by said delivery line to said drill stern, a mud ow rate sensing container communicating with said by-pass line and having an outlet discharging into said mud pit in a manner whereby to maintain a substantially constant level of mud in said container, a mud throttling valve provided in said mud return line, and means responsive to variations of the mud level in said container for actuating said return line throttling valve whereby to proportionately increase and decrease the flow rate and pressure of mud in said return line in coordination with increase and decrease in the ow rate of the by-passed mud.

References Cited UNITED STATES PATENTS 1,938,019 12/1933 Hild 175--25 2,786,652 3/1957 Wells 175-25 3,213,939 10/1965 Records 175-38 X 3,268,017 8/1966 Yarbrough 175-25 CHARLES E. OCONNELL, Primary Examiner.

DAVID H. BROWN, Examiner. 

